OLIGOTROPHIC LIFESTYLE ADAPTATIONS IN THE EASTERN MEDITERRANEAN SEA HETEROTROPHIC BACTERIA

The Eastern Mediterranean Sea is one of the most oligotrophic oceanic regions on Earth. Not much is known about its water column microbial community composition. Marine microorganisms play an important role in marine ecosystems by converting solar energy to chemical energy, catalyzing biogeochemical transformations of all nutrients and trace elements that sustain life in the ocean. There is a great anomaly between the amount of marine microbes that exist in the environment and that the amount that can be grown on agar plates (usually bacteria from the Eastern Mediterranean Sea by mimic the environment, characterize their phylogenetic, morphology, physiology and eventually their functional, using whole genome sequencing. High throughput dilution-to-extinction culturing (HTC) method was performed. Seawater sample was diluted with sterile seawater supplemented with nutrients and inoculated into 24 well Teflon plates to obtain a small and known number of cells per plate well (~3 cells per well). Out of the total measured number of cells in the sea water collected for this experiment about 1.67% of the total cell species were cultivated, including several new species of bacteria. Most of the species were related to the Alphaproteobacteria clade SAR11, the most abundant heterotroph in marine euphotic zones worldwide. Others were identified as a novel Verrucomicrobia (one of them found with 88% 16S rRNA gene identity to its nearest cultivated representative, Pelagicoccus croceus N5FB36-5(T)). Physiological and growth optimization experiment for Verrucomicrobia showed Glucose as main carbon source with highest yield of biomass. Presence of Proteorhodopsin gene in several isolates suggesting them as a Photoheterotrophs. The phylogenetic and physiology results so far providing life evidences to the diversity and the complexity of marine microbial community in one drop of water in one of the most oligotrophic and P starved oceanic regions.